Method of squeeze cementing a well



United States Patent- [72] Inventor John F. MllilllQldJI- 2.236.836 4/1941 Prutton l66/297X I Oalrmont. Pennsylvania 3.277361 10/1966 Bohn 166/297X [2|] Appl; No. 817,852 3.393.736 7/1968 Goodwin; 166/276 [22] Filed Aprllll, I969 3,428.l2l 2/l969 Harnsberger.. 166/276 [45] Patented Nov. 24, 19 70 1 3.327.783 6/1967 Ayers 166/276X [73] Asslgnee g company Primary Examiner Marvin A. Champion 1. I of i Assistant Examiner-Ian A. Calvert no Attorney- Meyer Neishloss. Deane E. Keith and Paul L. Tillson [54] METHOD Ol SQUEEZE CEMENTI NG A WELL 6 Clnlms. 2 Drawing Figs. 1

v x ABSTRACT: A well penetrating an unconsolidated formation ['52] its. C l- "1 1 166/276, is treated o prevent flow of unwanted fluids and sand into the 166/292 166/297 well by squeezing a slurry of ravel and oil into the formation 8 Elihu/02 through perforations in the well casing until the pressure in- [50] Field ofS eareh l66/276, creases to jus below the f a tu i pressure f the f ti v 28 l 2815) 298 and thereafter squeezing a small volume of a slurry of cement into the sand pack. After the cement has set the casing is per- 1 [56] forated at the desired level in the well. The quantity of cement UNITED STATES PATENTS is controlled so that it can be penetrated by the perforating 2.033.562 3/1936 Wells l66/297X device Q at; it: 1 4% an .4

METHOD or squeeze CEMENTTNGA' wa t.

This invention relates to a method of controlling the move merit of unwanted material from an unconsolidated formation into a well penetrating that formation and more particularly to a method of squeezing cement which permits subsequent perforation of casing in the well to place the well on production.

Many highly productive-oil-bearing formations are unconsolidated or incompetent. Those terms are used to identify formations whichdo not have physical-strength adequate to prevent the movement of formation particles into a well when the well is placed on production. The formation particles,

7 referred to as sand, may plug the well and thereby make In either event, it is necessary to control the movement of sand .into the well bore, and it is desirable and frequently necessary to reduce the rate of water production. There are numerous techniques for Controlling sand, but these methods are seldom effective in simultaneously reducing water production.

One method'that has been used to prevent the flow of undesired fluids into a well is squeeze cementing. 1n squeeze cementing a well having casing extending through the unconsolidated formation, a neat cement slurry or one containing additives is pumped down the well anddisplaced through perforations in the casing until the pressure on the well increases substantially to show that flow of the cement slu rry'into the formation is impeded. The optimum volume of cement to be squeezed is the minimum volume necessary toseal the channels and perforations. While this volume isnormally exceeded in practice, experience has shown that slurry volumes can be minimized in squeezing consolidated formations by use of retarded low-water-loss cements together with the hesitation technique. This procedure can also be used successfully. in treating wells completed in unconsolidated formations from which no formation sand has been produced. Frequently, however, squeeze cementing is done after a considerable volume of sand has-been produced into the well. in those instances, the volume of cement that is squeezed into the formation is usually at least the volume required to replace sand that found that the dense impermeable cement sheath formed when the cement sets extends farther out into the formation than the perforating device can penetrate, and the well cannot be placed on production.

This invention resides in a squeeze cementing method for the prevention of flow of unwanted materialsinto a well in which gravel is suspended in a nonaqueous liquid and displaced down the welland into an unconsolidated oil-bearing formation. Displacement of the gravel into the'formation is continued until the gravel bridges openings in the formation and around the casing and prevents further flow of the suspension into the formation. The gravel is followed by a small volume of cement slurry which is displaced into thegravel pack immediately adjacent the well and is held in place until the cement sets. Thereafter, the casing and cement sheath are perforated and the well placed on production.

In the drawings: 7 1

FIG. 1 is a diagrammatic vertical sectional view of the interval of a well having casing set through an unconsolidated oilbearing formation showing the condition of the unconsolidated formation before treatment in accordance with this invention.

FIG. 2 is a diagrammatic vertical sectional view of the well illustrated in FIG. 1 after treatment by this invention.

Referring to FIG. 1, an interval of a well indicated generally by reference numeral 8 is shown with casing 10 penetrating an unconsolidated formation 12 between cap rock 14 and base rock 16. The casing 10 is cemented in place in the customary manner by displacing a cement slurry down through the casing and upwardly through the annulus between the casing 10 and the borehole wall to form a cement sheath 18 in that annular space. After cementing, the casing 10 and cement sheath 18 are perforated as indicated by reference numeral 20 through the interval of the unconsolidated formation 12.

- During production of fluids from unconsolidated formation 12 through well 8, sand from the formation flows into the well. The flowof sand may result in the creation in formation 12 of one or more cavities 22 surrounding the casing. in some instances, channels 24 extending from the perforations 20 in the casing may penetrate a water zone 26 underlying oil in'the formation 12 with the resultant flow of water into the well.

. Usually flow of sand into the well occurs principally because of breakthrough of water from the water zone into the well or because of water damage to the formation that increases the concentration of ,water in the formation whereby the water becomes mobile. Such damage may occur as a result of the filtrationof water from drilling liquid usedduring the drilling of the well or from cement used to cement the casing in place. Theldamage to the formation usually extends for a distance of 2 to 3 feet radially from the well but may extend as far as 10 feet. While cavities 22 and channels 24 have been shown as being formed in the unconsolidated formation 12, damage to the formation does not always take that form. In some instances formation sands adjacent the well that flow into the well are replaced by movement of sands from farther back in the formation.

In the treatment of the well in accordance with this invention,- sand 27 which may .be accumulated in the well is removed by bailing or-circulation. Then, as-sho'wn in FIG. 2, a

packer 28 is run into the well on tubing 30 and set just above the perforatedinterval of the casing. A slurry of gravel, for example Ottawa sand particles having a size in the range of 20 to 40 mesh U.S. Series, suspended in a nonaqueous liquid such as kerosene, diesel oil or even a light crude oil, is pumped down the well through tubing 30 and displaced outwardly into the cavities 22 and channels 24. The suspension may contain 1 to Spounds of gravel per gallon of oil and preferably contains 1 to 3 pounds per gallon; The displacement is continued until the'pressure increases to a pressure just below that required to fracture the formation 12, at which time the cavities 22 and channels 24 should be bridged with gravel particles. If no cavities or channels have been formed, the suspension of gravel in oil squeezed into the formation moves undamaged sand that has moved toward the well back toward its original position. Squeezingis continued until the pressure approaches a level at which fracturing of the formation would occur.

The slurry of gravel and oil is followed by a slurry of hydraulic cement of which Portland cement is a preferred type. Pozzolanic cements also are suitable for use in this invention. The cements that can be used in the preparation of the novel compositions of this invention are described in the publication entitled AP-l Specification for Oil Well Cements and Cement Additives" (AP! STD l0-A, sixth edition, Jan. 1959) published by the American Petroleum institute. The cements are there defined as The product obtained by grinding clinker consisting essentially of hydraulic calcium silicates to which no additions, other than suitable set modifying agents, have been interground or blended during manufacture." A suitable set modifying agent is one which has no deleterious effect on the durability of the hardened cement and causes no retrogression in strength of the cement. Cements of classes A, B, C, N, D, E and F described on page 4 of the AP! specification are suitable. In addition to the common cements of those classes. the retarded and nonretarded slow set cements can be used. The preferred compositions, containing both retarding and fluid-loss agent. are similar to those described in the article Formation Cement Squeezes by Using Low-Water-Loss Cements". (H. 1. Beach, T. B. O'Brien and W. C. Goins, The Oil and Gas Journal, May 29 and June 12, 1961.) A 35 to 55 percent cement slurry can be used. The term percent" in defining cement slurry concentrations isused in the trade to designate the number of pounds of water per hundred pound sack ofcement.

The volume of cement slurry is carefully controlled to compact and impregnate the gravel pack with a slurry for a radial distance of approximately 6 inches from the casing. Care is taken to avoid impregnating the gravel pack with cement for a radial distance larger than can be penetrated with conventional perforating devices such as shaped charges. lmprcgnating with cement uniformly through the perforated interval for a radial distance larger than 9 inches should be avoided. This is best accomplished by use of the preferred cement compositions and the hesitation technique in which the displacement of cement is interrupted periodically. Excess cement is circulated out of the well and the well is then closed in to allow the cement to set. Thereafter, the casing 10 is perforated in the oil zone by conventional means and the well placed on production in the usual manner. If water production had been a condition to be corrected by the treatment, care should be taken to avoid perforating into the water zone. The shaped charges ordinarily used for perforating are capable of penetrating the casing and 9 to 12 inches of rock; hence, there is no difficulty in penetrating the cement sheath surrounding the well. Because the channels and perforations near the water zone are sealed with cement and gravel, water does not flow freely into the well. Also, because the gravel squeezed into the 1. A method of treating a well having casing penetrating an unconsolidated oil-bearing formation and perforations through the casing in the interval of the unconsolidated formation to prevent flow of unwanted materials into the well comprising displacing a suspension of gravel in an oil downwardly through the well and into the formation, squeezing the suspension into the unconsolidated formation to form' a gravel pack surrounding the well, squeezing a slurry of hydraulic cement into the gravel pack in an amount to fill voids in the gravel pack a radial distance less than the maximum penetration of perforating devices, allowing the hydraulic cement to set, and perforating through the casing and said set cement into said gravel pack.

2. A method as set forth in claim 1 in which the cement slurry is displaced from the well into the gravel pack in an amount adapted to cement the gravel pack for a radial distance of 6 to 9 inches.

3. A method as set forth in claim 1 in which the gravel has a size of 20 to 40 mesh U.S. Series.

4. A method asset forth in claim 1 in which the hydraulic cement is displaced into the gravel pack in a series of displacement steps separated by periods of holding the cement in place.

5. in a method of treating a well to prevent the flow of unwanted material into the well from an unconsolidated formation by consolidation of the formation with hydraulic cement. the improvement comprising displacing a suspension of gravel in an oil downwardly'through the well and outwardly into the unconsolidated formation to form a gravel pack around the well before consolidation of the formation with hydraulic cement, squeezing the suspension into the formation, and

thereafter displacing hydraulic cement from the well into the gravel pack in an amount adapted to cement the gravel pack for a distance radially from said well in the range of 6 inches up 'to the maximum distance penetrated by perforating devices.

6. A method of treating an oil well having casing extending downwardly through an oil zone in an unconsolidated formation to prevent flow of sand and water into the well, said casing having perforations in the interval of the unconsolidated formation, comprising removing sand from the well, displacing a suspension of gravel'in oil down the well and into the formation surrounding the well, squeezing the suspension into the formation tobridgeopenings in the formation and form a gravel pack around the well, displacing a slurry of Portland cement into the gravel pack to impregnate the gravel pack with a cement slurry for-a radial distance of approximately 6 to 9 inches, closing in the well while the cement sets, and thereafter perforating through the casing and said set cement into said gravel pack. 

